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International Concrete Abstracts Portal

Showing 1-5 of 31 Abstracts search results

Document: 

SP262-25

Date: 

October 1, 2009

Author(s):

T. Sowoidnich and C. Rößler

Publication:

Symposium Papers

Volume:

262

Abstract:

The hydration of tricalcium silicate (C3S), the major component of portland cement, determines setting and strength of concrete. Setting of portland cement pastes (that is, concretes) is strongly affected by the use of superplasticizers (SP). As it is commonly agreed, the hydration of C3S proceeds through a dissolution precipitation process. Thus, the present study investigates the dissolution behavior of C3S in dependence of SP addition. Dissolution experiments are carried out at paste conditions (w/C3S = 0.5) and at high liquid-solid ratio (w/C3S = 50). It is shown that in the presence of SP the ionic concentrations in the solution are shifted to lower calcium and higher silicon values. The reason might be a varied degree of C3S hydration, complex formation, or shifted ion concentrations due to the presence of ions introduced by SP addition (that is, Na). Additionally, calorimetric analysis clearly shows that in the presence of SP the dissolution heat of C3S is increased. It is concluded that in the presence of SP the dissolution of C3S is not diminished but rather unchanged or even increased.

DOI:

10.14359/51663243


Document: 

SP262-09

Date: 

October 1, 2009

Author(s):

K. Saito , M. Kinoshita, and H. Umehara

Publication:

Symposium Papers

Volume:

262

Abstract:

In order to develop a chemical admixture which improves durability of concrete, we have experimentally made two types of hybrid admixtures combining a single-liquid type, high-range, water-reducing admixture with a shrinkage-reducing admixture, and examined their concrete properties, ranging from normal - to ultrahigh-strength. Hybrid admixture, HSP1, for normal-strength concrete, showed reduced drying shrinkage of approximately 15 % and HSP2, for high-strength concrete, showed an autogenous shrinkage reducing ability of approximately 20~35 %. Also, both showed sufficient resistance to frost damage and carbonation.

DOI:

10.14359/51663227


Document: 

SP262-14

Date: 

October 1, 2009

Author(s):

Q. Ran, J. Liu, C. Miao, Y. Mao, Y. Shang, and J. Sha

Publication:

Symposium Papers

Volume:

262

Abstract:

A new class of polycarboxylate superplasticizer with a grafted pendant group of polyethylene oxide has been developed and extensively used in the construction field due to its outstanding water reducing ratio, high workability retention at small dosages and excellent compatibly with higher dosage rates of industrial by-products. Nevertheless, a drawback of this new generation superplasticizer is their effects in delaying the rate of cement hydration, especially when they are used at higher dosages and in low temperatures environment. These aspects limit their industrial application because of the slow mechanical strength development at the early age. In order to overcome this drawback, a new polycarboxylate superplaticizer (SSP) has been developed by means of optimizing the comb copolymer structure so as to meet ultra-early strength development requirements of construction projects. The results of mortar or concrete tests clearly indicate that SSP has the capacity to considerably accelerate the development of early age mechanical strength in conditions of low curing temperature, in comparison with the ordinary superplasticizers. The compressive strength of concrete containing SSP can reach 500% and 480% at an early age of 24 hours and 30 hours, respectively, when compared with ordinary polycarboxylate polymers at the same dosages. Engineering experimental results proved that the SSP can meet the requirements of concrete admixtures for high-speed railway construction projects.

DOI:

10.14359/51663232


Document: 

SP262-28

Date: 

October 1, 2009

Author(s):

M. Ohno, T. Sugiyama, T. Sugamata, and A. Ohta

Publication:

Symposium Papers

Volume:

262

Abstract:

Lignosulfonate-based air-entraining (AE) water-reducing agents have been used in various concrete structures for over 50 years. Polycarboxylate-based superplasticizers, which are the main superplasticizers in use today, have been on the market for 20 years and have recently been applied to various kinds of concrete structures. Therefore, it is important to know the difference that these three dispersants (lignosulfonate-based (LG), B-naphthalenesulfonate-based (BNS), and polycarboxylate-based (PC)) have on concrete durability. The authors, using superplasticizers containing each dispersant, studied the properties of concrete at a w/c of 0.50 up to the age of 20 years. This paper discusses the experimental results up to the age of 3 years following standard curing and artificial sea water curing, and under normal external exposure and exposure in a splash zone. As a result, no major difference has been observed in the effect on properties of the hardened concrete between PC and BNS, dispersants in superplasticizers. In addition, the authors consider that concrete incorporating PC-based superplasticizer or BNS-based superplasticizer has equal durability to that of concrete incorporating an AE waterreducing agent, most of which is in service over the long term.

DOI:

10.14359/51663246


Document: 

SP262-12

Date: 

October 1, 2009

Author(s):

J. Zimmermann, C. Hampel, C. Kurz, L. Frunz, and R.J. Flatt

Publication:

Symposium Papers

Volume:

262

Abstract:

Nowadays outstanding concrete performances are achieved using polycarboxylate-type superplasticizers. Nevertheless high performing superplasticizers are often sensitive to the cement used and in particular the cement sulfate content. Laboratory studies have shown that sulfates strongly influence the performance of superplasticizer because they inhibit polymer absorption which causes a reduction in flow properties of cementitious materials. This seems to have led to the belief that this phenomenon is generally true for polycarboxylates. In fact, it depends very much on the detailed polymer structure. In this study, the sulfate sensitivity of polymers with systematically varied polymer structures has been measured through paste experiments and the influence of different polymer structures on the sulfate sensitivity will be discussed.

DOI:

10.14359/51663230


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